It isn't. Unless someone was operating a crazy and expensive free guns charity, you are not "handing the gun to someone else". You are _reselling_ the gun to someone else who could not legally purchase or is avoiding a paper trail in order to commit a crime.

Sometimes that's even a crime without the inability to legally purchase or avoid a paper trail - just lying about the recipient and engaging in a private sale can be criminal even if both parties are eligible for the firearm purchase

https://en.wikipedia.org/wiki/Abramski_v._United_States

I didn't mean to imply that there wouldn't be a payment - although it's not always the case.

It's a thoughtcrime and a terrible law because of it. There's a ton of these w.r.t. gun laws in the US. Say the wrong thing and you get ten, say something slightly different and you get zero.

We examine intent for homicide too.